android: ensure image round down to at least 1 block

Signed-off-by: hmz007 <hmz007@gmail.com>

system/update_engine/payload_generator/generate_delta_main.cc

@@ -465,8 +465,9 @@ void RoundDownPartitions(const ImageConfig& config) {
     if (part.path.empty()) {
       continue;
     }
-    const auto size = std::max<size_t>(utils::FileSize(part.path), kBlockSize);
+    auto size = utils::FileSize(part.path);
     if (size % kBlockSize != 0) {
+      size = std::max<size_t>(size, kBlockSize);
       const auto err =
           truncate(part.path.c_str(), size / kBlockSize * kBlockSize);
       CHECK_EQ(err, 0) << "Failed to truncate " << part.path << ", error "